1. Field of the Invention
The present invention relates to a monolithic LC resonator and a monolithic LC filter, and more particularly, to a monolithic LC resonator and a monolithic LC filter for use in a high frequency wave band.
2. Description of the Related Art
FIGS. 16 and 17 show an example of a conventional monolithic LC resonator. As shown in FIG. 13, an LC resonator 100 includes a ceramic sheet 104 having a capacitor pattern 112 provided on the upper surface thereof, a ceramic sheet 105 having an inductor pattern 111 provided on the upper surface thereof, a ceramic sheet 106 having an input capacitor pattern 115 and an output capacitor pattern 116 provided on the upper surface thereof, ceramic sheets 102 and 108 having shield electrodes 113 and 114 provided on the upper surfaces thereof, respectively.
The ceramic sheets 101 to 108 are stacked, and fired to produce a laminate 110 shown in FIG. 17. On the laminate 110, an input terminal 121, an output terminal 122, and ground terminals 123 and 124 are provided. The input capacitor pattern 115 is connected to the input terminal 121. The output capacitor pattern 116 is connected to the output terminal 122. To the ground terminal 123, the lead-out portion of the inductor pattern 111, and one end of the shield electrodes 113 and 114 are connected. The lead-out portion of the capacitor pattern 112 and the other end of the shield electrodes 113 and 114 are connected to the ground terminal 124.
In the above-described LC resonator 100, an inductor including the inductor pattern 111, and a capacitor including a capacitor pattern 112 opposed to the open end of the inductor pattern 111 define an LC parallel resonance circuit. The LC parallel resonance circuit is electrically connected to the input terminal 121 via a coupling capacitor including an inductor pattern 111 and the input capacitor pattern 115 opposed to each other. Similarly, the LC parallel resonance circuit is electrically connected to the output terminal 122 via a coupling capacitor including the inductor pattern 111 and the output capacitor pattern 116 opposed to each other.
The characteristics of the LC resonator depend on the Q value of the inductor in the resonance circuit. The Q value of the inductor is expressed as Q=2xcfx80f0L/R, in which L is the inductance of the inductor, R is the resistance of the inductor, and f0 is the resonance frequency. As seen in this formula, the Q value of the inductor can be increased by decreasing the resistance R of the inductor. The inductance R is inversely proportional to the cross section of the inductor pattern 111. Hence, the Q value is increased by increasing the cross section S of the inductor pattern 111.
However, where the thickness of the inductor pattern 111 is increased to increase the cross-section S of the inductor pattern 111, the internal strain of the laminate 110 is substantially increased when the ceramic sheets 101 to 108 are integrally fired, resulting in delamination and other problems.
Further, a magnetic field generated in the periphery of the inductor pattern 111 is concentrated on the edge of the inductor pattern 111, causing a large eddy current loss. Moreover, in the conventional LC resonator 100, the magnetic field generated in the periphery of the inductor pattern 111 is interrupted by the capacitor pattern 112. Thus, the inductance L of the inductor is very low.
As described above, with the conventional LC resonator 100, it is difficult to attain a high Q value because the resistance R of the inductor pattern 111 constituting the LC resonance circuit is large, and moreover, the inductance L is low.
To overcome the above-described problems, preferred embodiments of the present invention provide a monolithic LC resonator and a monolithic LC filter each including an inductor having a high Q value.
According to a preferred embodiment of the present invention, a monolithic LC resonator includes a laminated body including an insulation layer, an inductor pattern, and a capacitor pattern laminated together, an LC resonance circuit provided in the laminated body includes an inductor defined by the inductor pattern, and a capacitor arranged such that the capacitor pattern is opposed to the inductor pattern with the insulation layer being sandwiched between the capacitor pattern and the inductor pattern. In the monolithic LC resonator, the inductor of the LC resonance circuit has a multi-layer structure in which a plurality of tubular structures are laminated to each other through the insulation layer, each of the plurality of tubular structures is defined such that at least two inductor patterns are electrically connected to each other through a via-hole provided in the insulation layer, and the capacitor pattern is arranged between the two tubular structures of the inductor.
Further, according to another preferred embodiment of the present invention, a monolithic LC filter includes a laminated body including a plurality of insulation layers, a plurality of inductor patterns, and a plurality of capacitor patterns laminated together, a plurality of LC resonators provided in the laminated body includes a plurality of inductors defined by the inductor patterns, and a plurality of capacitors arranged such that the capacitor patterns are opposed to the inductor patterns with the insulation layers being sandwiched between the capacitor patterns and the inductor patterns. In the monolithic LC filter, the inductor of each LC resonator has a multi-layer structure in which a plurality of tubular structures are laminated to each other through an insulation layer, each of the plurality of tubular structures is arranged such that at least two inductor patterns are electrically connected to each other through a via-hole provided in the insulation layer, and at least one of the capacitor pattern and a coupling capacitor pattern for capacitance-coupling the LC resonators is arranged between the tubular structures of the inductor.
The inductor preferably includes the plurality of tubular structures. The surface area of the inductor can be increased without increasing the thickness of the inductor pattern. In general, high frequency current has the properties that it is concentrated onto the surface of a conductor to flow, due to the skin effect. Because of this property, the entire inductor, of which the surface area is greatly increased, is effectively used as a path for high frequency current. Accordingly, the resistance of the inductor is significantly decreased as compared with that of a conventional inductor, and the Q value of the inductor is greatly improved.
A magnetic field generated with high frequency current flowing through the inductor does not substantially pass between the plural tubular structures constituting the inductor. Accordingly, the capacitor pattern and the coupling capacitor pattern for capacitance-coupling the resonators arranged between the two adjacent tubular structures in the laminating direction of the laminated body do not interfere with the magnetic field of the inductor.
Further, the inductor has the plurality of tubular structures, and the plurality of tubular structures are laminated through an insulation layer to define a multi-layer structure, which reduces the concentration of a magnetic field generated in the periphery of the inductor, on the edges of the inductor pattern.
Other features, elements, characteristics and advantages of preferred embodiments of the present invention will become apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.